Conventionally, intravascular diagnostic or therapy has been conducted by inserting a catheter into a blood vessel using light for diagnostics or therapy. For example, a vessel lumen has been observed with an angioscope by irradiating illumination light. Furthermore, angioplasty or the like has been conducted by irradiating a vessel lumen with high-intensity pulsed light such as laser light. However, when light is irradiated into the blood vessel while blood exists in the blood vessel, light having a wavelength of visible light to ultraviolet light is absorbed by hemoglobin in the blood and infrared light is absorbed by water. For this reason, it has been difficult to allow light to reach the region of the blood vessel targeted for diagnostics or therapy. Therefore, there has been conventionally a necessity for use of a balloon such as a blood flow shut-off balloon to shut off a blood flow for intravascular diagnostics or therapy or for contact irradiation by causing the region to be irradiated with light for diagnostics or therapy to contact the region of the blood vessel having disease or trouble. For example, when an intravascular lumen is optically observed, it is necessary to remove blood inside the blood vessel which obstacles the field of view in the region observed, and therefore the blood flow is temporarily stopped using a shut-off balloon or by injecting a transparent fluid such as saline with heparin into a region to be observed in the blood vessel and replacing the blood in the region to be observed with the transparent saline or the like (see Patent Document 1 and Patent Document 2).
However, when the blood flow is stopped using the shut-off balloon, a hemostasis time for avoiding ischemia is limited and it is not possible to secure a sufficient time for diagnostics or therapy. Use of the balloon cannot completely shut off the blood flow, either.
Furthermore, contact irradiation of light also requires special means for causing an irradiation section to contact the intravascular lumen wall and needs to avoid excessive contact so as not to damage the blood vessel wall.
Moreover, when the field of view is secured by removing the blood in saline using a conventional angioscope, even a small amount of blood is mixed in, illumination light is diffused and reflected, which obstructs the field of view considerably. This causes a vicious cycle of requiring further injection of a large amount of saline.
Furthermore, these conventional methods stop a blood flow or inject a large amount of foreign matters into the blood vessel, blocking the circulation of blood, which is an oxygen carrier, preventing a sufficient amount of oxygen from being supplied to peripherals and thus presenting a high level of invasiveness against an examinee. The influence of the exclusion of blood in the coronary artery is particularly large and it is necessary to practice the conventional methods within a limited time while always monitoring ischemia with an electrocardiogram, and in this way, operation of the coronary artery endoscope involves many difficulties.
On the other hand, a method of observing a state of intravascular lumen using ultrasound (Intravascular Ultrasound: IVUS) instead of light is also being widely practiced. While this method is minimally invasive, it is not a method intended to directly observe an intravascular lumen and it is unable to obtain information on color tone, and it is difficult to provide precise characteristic diagnostics of lesioned parts. Especially in the case of a coronary artery disease, it has been impossible to distinguish yellow atheroma which provokes acute transmural myocardial infarction due to intimal breakdown from white atheroma in which fibrosing advances without producing intimal breakdown.
As shown above, the conventional methods cannot provide any precise and safe diagnostics or therapy on a coronary artery lumen in particular.    Patent Document 1 JP Patent Publication (Kokai) No. 6-296695 A    Patent Document 2 JP Patent Publication (Kokai) No. 11-262528 A